Optimization and Control of a Hydro-Mechanical Transmission based Hybrid Hydraulic Passenger Vehicle

Hydro-mechanical transmission (HMT) based hybrid hydraulic vehicle architecture is potentially more efficient than other architectures because: 1) it uses the efficient mechanical transmission for partial power transfer, 2) it allows the engine to operate at its most efficient point. The input coupled power split hybrid vehicle being developed is one such example. The increase in degrees of freedom makes design, control and analysis more challenging. In this paper, HMT hybrid vehicle dynamics are derived and decomposed explicitly into decoupled dynamics that relate to vehicle motion and to efficient vehicle operation. A three level hierarchical control and analysis architecture is then introduced that separates the vehicle operation into a drive cycle dependent optimization layer, a non-drive cycle dependent optimization layer, and real time control layer. Exercising this framework indicates that to improve fuel economy, the current vehicle design can benefit from allowing pump/motor lock up, improved pump/motor efficiencies and improved sizing.